convert : handle max_target_positions (#2477)

as needed eg for
https://huggingface.co/primeline/whisper-large-v3-turbo-german/blob/main/config.json

models/convert-h5-to-ggml.py

@@ -82,7 +82,11 @@ def bytes_to_unicode():
 
 encoder = json.load((dir_model / "vocab.json").open("r", encoding="utf8"))
 encoder_added = json.load((dir_model / "added_tokens.json").open( "r", encoding="utf8"))
-hparams = json.load((dir_model / "config.json").open("r", encoding="utf8") )
+hparams = json.load((dir_model / "config.json").open("r", encoding="utf8"))
+
+# Add this block to handle missing 'max_length'
+if "max_length" not in hparams:
+    hparams["max_length"] = hparams.get("max_target_positions", 448)
 
 model = WhisperForConditionalGeneration.from_pretrained(dir_model)